Page 78 - Synthetic Fuels Handbook

FUELS FROM PETROLEUM AND HEAVY OIL 65

TABLE 3.1 Crude Petroleum Is a Mixture of Compounds That
Can Be Separated into Different Generic Boiling Fractions

Boiling range*
Fraction °C °F
Light naphtha −1–150 30–300
Gasoline −1–180 30–355
Heavy naphtha 150–205 300–400
Kerosene 205–260 400–500
Light gas oil 260–315 400–600
Heavy gas oil 315–425 600–800
Lubricating oil >400 >750
Vacuum gas oil 425–600 800–1100
Residuum >510 >950

*For convenience, boiling ranges are converted to the nearest 5°C.

To convert crude oil into desired products in an economically feasible and environmen-
tally acceptable manner. Refinery process for crude oil are generally divided into three
categories: (a) separation processes, of which distillation is the prime example; (b) conver-
sion processes, of which coking and catalytic cracking are prime example; and (c) finishing
processes, of which hydrotreating to remove sulfur is a prime example.
The simplest refinery configuration is the topping refinery, which is designed to prepare
feedstocks for petrochemical manufacture or for production of industrial fuels in remote
oil-production areas. The topping refinery consists of tankage, a distillation unit, recovery
facilities for gases and light hydrocarbons, and the necessary utility systems (steam, power,
and water-treatment plants). Topping refineries produce large quantities of unfinished oils
and are highly dependent on local markets, but the addition of hydrotreating and reforming
units to this basic configuration results in a more flexible hydroskimming refinery, which
can also produce desulfurized distillate fuels and high-octane gasoline. These refineries
may produce up to half of their output as residual fuel oil, and face increasing market loss
as the demand for low-sulfur (even no-sulfur) fuel oil increases.
The most versatile refinery configuration today for fuel production is the conversion
refinery. A conversion refinery incorporates all the basic units found in both the top-
ping and hydroskimming refineries, but it also features gas oil conversion plants such as
catalytic cracking and hydrocracking units, olefin conversion plants such as alkylation
or polymerization units, and, frequently, coking units for sharply reducing or eliminating
the production of residual fuels. Modern conversion refineries may produce two-thirds of
their output as unleaded gasoline, with the balance distributed between liquefied petro-
leum gas, jet fuel, diesel fuel, and a small quantity of coke. Many such refineries also
incorporate solvent extraction processes for manufacturing lubricants and petrochemical
units with which to recover propylene, benzene, toluene, and xylene for further process-
ing into polymers.
Finally, the yields and quality of refined petroleum products produced by any given oil
refinery depends on the mixture of crude oil used as feedstock and the configuration of the
refinery facilities. Light/sweet crude oil is generally more expensive and has inherent great
yields of higher value low-boiling products such as naphtha, gasoline, jet fuel, kerosene,
and diesel fuel. Heavy sour crude oil is generally less expensive and produces greater yields
of lower value high-boiling products that must be converted into low-boiling products.
This chapter presents an overview of petroleum refining in order for the reader to place
each process in the correct context of fuels production.